1. Field of the Invention
The present invention relates generally to a fluid-filled elastic mounting structure, and more particularly to improvements in such a fluid-filled elastic mounting structure, in the durability and vibration damping and isolating characteristics.
2. Discussion of the Prior Art
Recently, a so-called fluid-filled elastic mount has been increasingly used as an elastic mounting device for flexible connection of a given member to a support structure, for example, an engine mount for flexible mounting of a power unit of a motor vehicle to the body of the vehicle. Such a fluid-filled elastic mount is adapted to damp and isolate input vibrations, based on restricted flow of a non-compressible fluid through a restricted passage, between two fluid chambers defined within the structure of the elastic mount.
Described more specifically, a generally used fluid-filled elastic mount of the type indicated above includes an elastic body made of a rubber material, which elastically connects a first and a second support member which are disposed opposite to each other in a mutually spaced-apart relation in a load-receiving direction in which a major vibrational load is received. A fluid chamber is defined between the elastic body, and a closure member which includes a flexible portion and which is secured to the second support member. The fluid chamber is filled with a non-compressible fluid. The fluid chamber is divided by a suitable partition assembly, into a pressure-receiving chamber formed on the side of the first support member, and an equilibrium chamber formed on the side of the closure member. The elastic mount has suitable means for defining a restricted fluid passage for restricted fluid flow between the pressure-receiving and equilibrium chambers.
Upon application of a vibrational load to the elastic mount, the volume of the pressure-receiving chamber is changed due to elastic deformation of the elastic body, and the fluid pressure in the pressure-receiving chamber is accordingly varied. As a result, the non-compressible fluid is forced to flow through the restricted fluid passage, between the pressure-receiving and equilibrium chamber, due to the change in the pressure in the pressure-receiving chamber, relative to that in the equilibrium chamber. Since the volume of the equilibrium chamber is variable due to a displacement of the flexible portion of the closure member, the pressure in the equilibrium chamber is maintained substantially constant when the fluid flows into and from the equilibrium chamber. In this arrangement, the input vibrational load having a frequency over a range to which the restricted fluid passage is tuned can be suitably isolated, based on the fluid flows through the restricted passage, or on resonance of the fluid mass in the mounting structure.
When the fluid-filled elastic mount is installed in position, the weight of a given member which is flexibly mounted on a support structure through the elastic mount acts on the mount in the load-receiving direction. Where the elastic mount serves as an engine mount for an automotive vehicle, a considerably large weight of the power unit including an engine is applied to the engine mount. Therefore, the pressure in the pressure-receiving chamber is considerably increased, and the volume of the equilibrium chamber is accordingly increased with an excessive degree of displacement of the flexible portion or flexible diaphragm of the closure member. This phenomenon deteriorates the durability of the flexible diaphragm, and consequently causes a relatively low level of durability of the fluid-filled engine mount per se.
Further, the expansion of the equilibrium chamber due to the static load acting on the elastic mount as described above inevitably requires the elastic mount to be large-sized, in order that the amount of volumetric change that may take place in the thus expanded equilibrium chamber upon application of a vibrational load to the elastic mount is sufficient to absorb or accommodate an increase in the pressure in the pressure-receiving chamber which is caused by the received vibrational load. If the amount of volumetric change of the equilibrium chamber indicated above is insufficient, the fluid may be inhibited from flowing from the pressure-receiving chamber into the equilibrium chamber, when the magnitude of the input vibration is extremely large. In this case, the elastic mount will not provide a desired vibration isolating effect.